I posted these in a CopTalk thread. Basically ... There is this Franken-15 design here I replicated from my carbine upper and rifle lower. A buddy is curious about trying this out, as he keeps his 6 position stock all the way out on his duty carbine(he is bigger than Lurch) anyways , and likes the solid A2 better. AR15 expert types, will he need to use the rifle buffer, or the carbine buffer and springs, etc? I thought it was as simple as swapping the upper to the rifle lower, but I told him I'd find out. Gotta admit, the look kind of grows on you. Thanks for the help, I told him I would try to find out. I messed with the franken carbine in the pictures a little around the house, and it wasn't too bad feeling.